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Have any large aeroplanes been landed — safely and without damage — in locations that they could not be flown away from?
And, what was done with them subsequently?

I was going to nominate the Gimli Glider, since it was only minimally damaged.  But refreshing my memory, it turns out there was enough straight-line on the racetrack to take off from, so they just patched it up and flew it out.  Noted for reference in case it occurs to anyone else.

Loosely related question about "can an airplane ever be stranded while airport construction/closure is occurring"? : https://aviation.stackexchange.com/questions/31802/can-planned-runway-closures-prevent-a-plane-from-leaving-an-airport

this question got now 20 answers. I am protecting it because the answer seems to be unequivocally "yes", and no more examples are needed. If people feel like a complete list is needed, the answer that will be accepted can be turned into a wiki answer.

Quite a number of the answers here are, while interesting, about cases where "...then they flew out the next day", in other words quite clearly not examples of having landed in locations from which the plane could never take off again!

@Daniele feel free to flag them as "not an answer" and leave a comment about that

My problem with the answers to this question is that the poster specifically said "With no damage" if its fixed on the ground, that doesn't qualify. The shuttle was designed to never take off from where it landed. Anything military is stripped down and has JATO strapped to it. Any plane that was landed WITHOUT DAMAGE would have been dismantled if it could not be flown away. That of course leaves the numerous occasion where a plane is intentionally flown someplace for a static display. Those come closeest.

what's a large aircraft, I've seen a few highway landings...

TACA Flight 110 made a deadstick landing on a grass levee. Engines got replaced and it took off using a nearby NASA facility.

https://en.wikipedia.org/wiki/TACA_Flight_110

How did they get it there?

@Skyler Gravity mostly

@Skyler "The aircraft was towed from the levee to the nearby NASA facility", from the wikipedia article linked in the answer.

+1 This, to me, is the best answer so far. Other answers mainly point out airplanes that were never intended to be flown again, landed in their locations purposefully without passengers and then turned into museums. I think this example is what OP was looking for.

@mattumotu And a hack of a luck! And for their sake, a hack of a skill too!

It's a quite interesting story. Without any thrust and low on altitude, the pilots intended to ditch the plane in the river until the levy presented itself as a less risky option.

This flight was also featured on the "Air Crash Investigations" TV programme which used the FVR and ATC recordings.

Landed without damage is specified in the question.  If the engines needed to be replaced, I don't think this qualifies.

They failed after flying into a blizzard, they weren't damaged on landing ;)

@Devilscomrade: Rainstorm, not blizzard, but yeah.

Sure!
An Ex-Interflug Ilyushin Il-62 was landed on the 900 m runway of Stölln/Rhinow airport (EDOR) in the German countryside in 1989 to be turned into a tourist attraction. Here is a short video of the event. As can be witnessed from the clouds of dirt, the pilot Heinz-Dieter Kallbach wasn't too concerned about using reverse thrust - the engines were not meant to run ever again.
If the Dornier Wal counts as a large aeroplane (it certainly did in its time), the two Amundsen airplanes N-24 and N-25 qualify also, one even twice: Both were used in 1925 for an attempt to reach the north pole by air but had to make an emergency landing on ice near the 88th parallel. Since N-24 had suffered damage during take-off (it had sprung a leak), it was left on the ice when Amundsen and his crew flew back with N-25 after having built an emergency runway in weeks of hard work in which they moved an estimated amount of 500 tons of snow. N-25 went on to make a historic East-West atlantic crossing in 1930 and was again landed successfully in a location from where it could not take off in 1932 - this time on the snowy banks of Isar river in Munich in order to be put on display in a museum (picture source).

Another memorable example is the Spantax pilot Rodolfo Bay who in 1967 mistook the Finkenwerder airport for Hamburg Fuhlsbüttel airport. He landed his Convair Coronado 990 on a runway (1360 m) which was technically too short for the landing (1650 m according to the flight manual). He even managed to fly the empty bird to Fuhlsbüttel - again with less runway than technically required.

Landed without damage is specified in the question. The first two fail.

@WBT: For the second one, N-24 was damaged during takeoff, not landing, and N-25 couldn't be flown out again until they built it a new runway, so it looks like it counts.

N-25 is the third example, and I still think the N-24 fails because of the damage regardless of when that damage occurred. However, if the N-24 helps tell the story motivating N-25, it might still fit in the answer.

The various Space Shuttle Orbiters did this all the time.
They mostly got piggyback rides back to their launch facilities.

I love the lateral thinking on this one. Not sure the shuttle is an aeroplane, but...

@T.J.Crowder I think for the purposes of this question, we can be generous and consider the Orbiter to be an overweight glider with a really, really, really poor (for being used as a glider) L/D ratio.

@aCVn - Yeah, I considered saying "Not sure the shuttle is an aeroplane so much as a brick with a slightly improved glide ratio..." but I felt like I was taking a potshot at the orbiter. :-)

I dont think the Orbiter qualifies for the spirit of the question. The shuttle Orbiter was not intended to ever take off normally, under its own power from anywhere, no matter where it landed. It was really a rocket glider.  The term "large aeroplane" used is unfortunately way too broad.

It just needed two JATO bottles, droppable fuel tank and D check before every flight.

@aCVn well in that case a cannonball can be considered a really really poor missle with bad propulsion. You're really stretching things.

@aCVn a cannonball is a glider, At least the shuttle has engines, but yes the Space Shuttle was not designed for horizontal take off. Massing at nearly 4.5 million lbs. it would need more than 2 JATO bottles to move on the runway. So anyplace the shuttle landed it was unable to take off -- by design.

@RowanHawkins: I think he was talking about these RATO bottles.

An Aerolineas Argentinas' Boeing 737-200 was hijacked by terrorists in 1975 and made to land in a farm. The government took 10 days to unstuck the aircraft from the mud and to move and install a makeshift aluminum runway (a mesh-like thing that was usually used for ice operations) and take-off at less than minimum weight.
The first officer was a glider pilot (I knew him personally, although we never spoke about this episode), so he was used to landing on random fields. A bit different than with a glider, though!

That's a lot of smoke coming off that aluminum runway.

You know that's dirt, right?

What about the "...installed a makeshift aluminum runway" part?  Regardless, I was being just a tad facetious. ;-)

Maybe I should have clarified that: it was more like a mesh. I'll edit.

How did you know him?

@Cloud:  not sure how it's relevant, but through gliding competitions and committees.

A B52 is pretty big right?
When a B52 was acquired by the Imperial War Museum, Duxford (a former second world war airbase now museum with a 1500m runway). They had to use chutes and a few practice flybys before landing. It's now on permanent display.
They had to do the same with a Concorde I believe!
Video:

Duxford's Concord was the last aircraft to land there before the runway was shortened to accommodate the construction of the M11 motorway.  I believe the post-M11 runway would have been too short for Concord to land.  Pre-M11, the runway was 1829m.  Duxford's website report the current runway has a usable length of 1199m.

I moved to Cambridge in 1999.  I thought something looked odd about that video, and then I realised - there's no M11 at the end of the runway!

Shortening the runway after the landing is cheating!

@Rich I don't think either could have taken off even from the original runway. The shortest I know of a Concorde taking off from is Leeds-Bradford, which is 2200m+.

Doesn't the B-52 need the chute even for a normal landing?

A war-surplus B-17, named "Lacey Lady", was landed on an Oregon highway to be converted into a roadside restaurant and fuel station.  I suppose it could have taken off from there again, if anyone had been suitably inclined…
There have also been several incidents where an airliner made an emergency landing on runways or fields that were below normal minimum standards, but by careful management of takeoff weight and other risk factors, was successfully flown out again.  Notable examples include TACA Flight 110 and the wrong-airport landing of the Dreamlifter at Jabara.

Those are all examples of the exact opposite of the what the question asked for - cases in which landings were made (whether planned or forced) into locations that meant the plane could never leave again by flying away.

Well, The TACA 737 landed on a grass field, and then it was towed to a nearby former runway which happened to be there by chance. I think it is the most appropriate answer here.

Downvoted for the second paragraph -- all those incidents fail the "could not be flown away from" criteria.

The Alraigo Incident https://en.wikipedia.org/wiki/Alraigo_incident
Harrier had to land on a container ship after running out of fuel.
Could potentially have flown it off if refueled and re-watered (for engine cooling in VTOL) but would also have had to be recovered to a suitable position as it slid and landed on top of a van.
Ship ended up sailing into harbour with the jet still on board.

This was damaged then? The OP is looking for UNDAMMAGED.

Doesn't sound damaged if it just slid back and rested on a van.  Maybe some minor damage, but probably not "can't fly again" level.  Wikipedia said it was "salvageable", but that's a little vague.

@RowanHawkins one of the articles linked from wikipedia shows the aircraft. It appears in good nick, just positioned really awkwardly. Maybe some scrapes and dents, nothing a lick of paint and some filler and a carpet knife won't fix :)

It definitely flew again - here is some history of the aircraft.  https://web.archive.org/web/20150806043252/http://www.airsceneuk.org.uk/oldstuff/2006/newarkshar/shar.htm  The incident is described a little over halfway down the page, alongside the third image.  It barely damaged the van, let alone itself https://www.airspacemag.com/military-aviation/oldies-amp-oddities-the-alraigo-incident-10366728/

Qantas landed 747 for a museum on a 1800x30m runway.
https://www.abc.net.au/news/2015-03-08/qantas-jumbo-arrives-at-wollongong/6288748

I'm pretty sure an empty 747 with just enough fuel to make it to the next larger airport could easily take off from a 1800m runway again.

@Bianfable depends on the runway strength. That does of course also become a factor in the landing.

If you can't land and takeoff a pretty much empty 747 from an 1800m runway, go home. Have a drink. Consider what else you might do with your life. :)

@jwenting I would think runway strength would be much more a concern on landing than taking off. The airplane puts less weight on the runway during takeoff than it puts on the ramp just sitting there.

@JuanJimenez Yeah, the roll of the KLM 747s at Princess Juliana was only slightly more than that full of passengers, cargo, and enough fuel to cross the Atlantic with reserves.

KLM flew a Fokker 70 to Lelystad (EHLE) airport to become part of the museum collection there. It wasn't legal to take off from there, though it probably could have managed (business jets use the field at times).
They for a while considered flying a 747 there to the same museum but this was not done because the runway wasn't strong enough to take the aircraft's weight. It could have landed within the runway length (damaging the runway in the process), but could never have taken off again. In the end the 747 was dismantled and transported on barges and trucks, then reassembled at the museum where it still stands today (and can be rented out as a venue for receptions).

Not sure if "large" enough, but most planes from an aircraft carrier need to be "catapulted" in order to takeoff, not just "flown" (although they also usually land with aid from an arrestor)

Nice idea - a bit of a frame challenge for the definition of "take off" to include whether it can do it under its own power. :)

This answer wins.  Many aircraft could land unarrested on an aircraft carrier and have no hope of taking off again- haven't there been Soviet defections this way?  I bet if a P-3 Orion had "the Nimitz or the sea" to choose from, they could get it stopped in the available deck, but it would come off by crane.

@Harper now try that with a P-8 :)

A Boeing 727-100 was landed at Meigs Field in Chicago (runway length 1,189 m) in 1992.  It was then loaded onto a barge and (eventually) installed as an exhibit at the Museum of Science and Industry, where it remains to this day.
It is not clear whether the 727-100 could have taken off again from this runway.  In one of the news interviews linked above, the pilot who landed the plane jokes that if he had to try it, he'd want to chain the airplane down at one end of the runway, run up to full power, and then cut the chain.

Speaking of Meigs Field... 16 planes became unable to take off from there on March 30, 2003.

"chain the airplane down at one end of the runway, run up to full power, and then cut the chain" I wonder why a standard short-field take-off would be any worse from a takeoff performance perspective, but that's a different question.

The Boeing 727 was designed to take off legally from a 4500-foot runway.  If you don't care about your safety margin, the 3900-foot runway of Meigs Field isn't a problem.

@fooot : If that had been an Answer (with a reference), I would have upvoted it.  (It's not a comment as it does not suggest an improvement to Michael Seifert's answer.)

Boeing 747 G-BDXJ (wikipedia link) landed in Dunsfold Airfield on 25 May 2005. Dunsfold runway is listed as 5,496ft (1,675m). I suppose it may be feasible to take off on that runway, but that wouldn't be easy. That 747 was never intended to fly again anyway.

They've also swapped off the engines now. Don't think it's happening

Yep.  I've actually been inside that plane. The engines seem fake anyway.  As far I could tell, that airframe doesn't have engines any more.

I've not been in - but I can see it out my window :-)  I think they were sold for a decent amount

How large is "large"?
I grew up just south of E.W. "Cotton" Woods Airport, a 2400' runway in Columbia, MO. My father told me some time in the 1970s that a jet-powered aircraft (I remember him saying a Learjet, though that could have been him using the name generically) had made an accidental or emergency landing at the airport, and needed to be hauled out on a flatbed after having the wings removed.
A Google search just now did not turn up anything about this, and I don't know how or where to search official incident reports to confirm.

If you know the exact airport involved, perhaps by airport identifier, and have a rough idea of when it happened, you could contact the NTSB (because it'd be in the US) and ask. If it happened in the 1970s, they should have a record of it, though it might not have been digitized.

There is no record on the NTSB database of any incidents or accidents involving a Learjet in Columbia MO in the 1970's.

Large would probably mean a “large transport category” aircraft certified under 14 CFR 25 or equivalent. Any Learjet (and most jets) would fall under that definition.

It seems the original learjet had a MTOW 1kg under the threshold for "transport category". Later models were heavier though.


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How do aircraft go off-course even with all their guidance technology?
Pilots today have more than enough technology both in the cockpit and in the infrastructure that supports them to know with great precision where they are at any given time. How/why do they still sometimes go off-course?

Haven't seen all the details from this one, but last time we've seen two conflicting accounts of what happened. Did they cross the border? Did they not? How far? How long? Unless you were actually on site with the right equipment to precisely determine the position of the aircraft at all times, it's just wild speculation on who is right.

They enter in others space because they want to. They know they are in.

@mins It is not a political game. I can accept that the vast majority, if not all, of modern airspace violations are intentional, but voting to close without the slightest attempt to explain technically how unintentional violations could happen or why they should not happen is a total non-answer. My question is not meant as flamebait.

@mins Would it have made any difference if I phrased my question as, "How would it be possible for aircraft to unintentionally enter another country's airspace?" Because that is essentially what I am asking.

I edited the title and removed military references.

The new phrasing of the question is a bit too generic IMHO... Reference to specific cases would narrow it down (there are many possible causes for going off-course, from intentional, hijack, incorrect info, problems with instruments, crew incapacitation, inattentive crew, sleeping crew...).

Are you also interested in the vertical navigation error (altitude error)?

1) Technology is fallible.
2) Humans are fallible.
Now that aircraft have GPS receivers it is rare for them to be off course by a considerable margin. That said, technology can fail and there are cases where the GPS cannot, or should not, be used.
The crew can also make mistakes, either by incorrectly reading the navigation data or by incorrectly entering flight path details into the navigation system: An aircraft may actually be 'on course' based on what the crew told it to do, but they told it the wrong thing. Depending on how data is entered into the system it's easy to add the wrong waypoint (some have very similar names, there's been a few cases of that happening) or to enter reciprocal bearings or lat/lon points.
On top of that there's simple crew distraction - if they're manually flying then they may be focussing on something else and not notice that are off-course: As happened on the Sukhoi superjet demonstration flight a few years ago.

@ Simon: in your great answer you mention crew distraction as a possible cause of getting off-course. Not sure if it's always to be called distraction. After all the golden rule is first flying the aircraft, which can be quite a job sometimes. Then comes navigating it. (And then communicating.)

@RobVermeulen: Yes, that's a good point. To be honest 'distraction' was simply the best word I could think of to describe this. Flying might be most important, but it is still a distraction from the navigation task :)

And to add to #2... people will sometimes hand fly the aircraft and just flat out forget to look at the map: sometimes if they think they know where they are but are in fact in a very similar looking area. I've done this when driving before I realised there are two very similar looking churches next to two very similar looking garages...

Thanks for the answer. I would be interested in knowing in what kind of situations GPS is not recommended.

@Pedro - ask another question! Sounds like a valid one to me.

@Pedro - another question regarding GPS is better I think. Whilst linked to this question it raises a number of different issues that aren't relevant to this answer.

The navigation data (angles, coordinates) are initially numbers and must be read by human first to use the navigation systems. If the pilot misreads or wrongly interprets the initial data, the navigation tools cannot help.
This seems the reason of both Varig Flight 254 and TWA Flight 3 navigation mistakes. In general cases seem rare as they require the navigators to stay disoriented for a long time, regardless of that they see, radio stations they hear, etc, etc.

My Dad was a fighter pilot in the Korean War. He acidentally did something in the cockpit which effected his air mix. Without sufficient oxygen, my Dad got lightheaded and started flying towards North Korea. My Dad might well have died or become a POW except that members of his fighter group flew back to find him. My Dad was sufficiently cognitively aware to recognize his comrades and use them as his "navigators" back to home base.
Things that can effect a pilot's cognitive state can still happen. Look at naval and air force fighter crashes over the past handful of years. As a chemist, I'd identify one likely culprit as new cockpit materials insufficiently tested for offgassing (changed chemical state) at critical state points. I have one material, in particular, in mind.

Out of curiosity, which material and why?

A basic expansion of os1’s answer.
1) broken or defective equipment.
2) equipment that is not properly maintained or calibrated.
3) improper use of equipment by flight crew.
4) incorrectly interpretation of output data from equipment by flight crew.
5) terrestrial or satellite navaids needed to operate equipment either down for maintenance or unavailable.
6) incorrect procedures used by flight crew.
7) Overconfidence in onboard systems causing negligence of basic airmanship and good risk management.
8) Confusion among duties for pilots in aircraft requiring more than one flight crewmember.
9)  saturation by existing cockpit tasks causing negligence in navigation.
10) human frailty, fatigue and external pressures.
It can happen to anybody, in any kind of airplane, no matter how advanced the equipment on board is.   I wrote in a post about Instrument flying that modern integrated flightdecks i.e. glass cockpit have the capability to make a good pilot better and a poor pilot dangerous.   This still rings true today.   Smart people routinely do stupid things in aircraft and it can have tragic consequences.   This can be insidious if one is not careful.

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What is the aircraft model used in the film "American Made"?
In American Made, what is the model of the white airplane that the CIA presents to Barry Seal (played by Tom Cruise)? He says something along the lines of "the fastest piston twin". Are those continental engines?

You can use IMPDb for aircraft in movies (and users of this stack can contribute to it).

If you are talking about the one prevalent in this trailer its an Piper Aerostar 600. The tail number is legitimate and the full registration details for 164HH can be found here.
Some of the movie may also have utilized a Beech Queen Air Model 88

It is an Aerostar, most likely the fastest GA piston twin ever, except for its little sisters and brothers, the 602   602p   700 series.   It was designed by  visionary Ted Smith.  Its airframe is strong enough to support turbopops and jets, which Smith envisioned for the future.    A slick, fuel efficient plane, very strong.   Large wing loading makes it cut through turbulence like butter.   Underwear changing sink rate, so have to keep them fast.   Probably my favorite of my imaginary planes I have not yet flown in real life.

The very plane from the movie crashed on Sep. 11, 2015 in Colombia.

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Is the autorotation in San Andreas movie realistic?
San Andreas is an awful movie, but given how helicopter-centric its plot is I'm wondering if they even got the autorotation landing correct?  In the middle of the movie the hero is cruising in (I think) a Bell 412 when the engines fail.  He tells his passenger they're going to autorotate, and he proceeds to do the following maneuver three times: Precipitous pitch down, then after picking up a lot of speed, a flare.  (The final "landing" flare is attempted in a crowded parking lot where he tries a last-second evasive maneuver that destroys the helicopter.)
My understanding is that a proper autorotation always simply consists of pitching to a specified glide path and not changing pitch until the landing flare.  Do any conditions or rotary-wing vehicles call for a different autorotation maneuver?

I can't find a clip online.  If he dives immediately, then it's unrealistic.  If he dives after entering autorotation, and the airspeed is low, then it could be realistic.  There is nothing stopping you diving (increases airspeed and rate of descent whilst reducing rotor speed) and flaring (does the opposite) as many times as you want but diving and flaring reduces distance travelled and time in the air since it's all about converting one form of energy into another.  As you say, you would normally select pitch for max range or minimum descent rate, leave it there and flare at the bottom.

If your first action is to pitch forward, then you die.  The rotor speed will drop to an unrecoverable speed very quickly.

I found it.  Complete nonsense.  Read this

Hopefully you were just interested in this particular scene, and you're not ok with the opening sideways dive into the cliff when rescuing the climber?  Wish I could find that clip.

@JPhi1618 - No kidding.  Most of the movie required extreme suspension of disbelief, logic, physics, etc.  I guess I had hoped that since they obviously had access to real helicopters and pilots, and somehow picked up the word "autorotate," maybe they'd at least ask someone to demonstrate a realistic autorotation in the helicopter they were filming.  Maybe they did and decided it just wasn't exciting enough for audiences....

Heh, yea.  That's ok - if the helicopter was depicted as poorly as computers are in movies, it would fly with the main rotor facing forward and travel at about 800mph before kicking in the turbo boost.

"Is [some aviation-related occurrence] in [some movie] realistic?" No.

Let's see how many things we can find wrong.

There's a bang, smoke starts coming from the exhaust.  Master caution comes on and his first response is to tap and check the 115v AC gauge!  The pilot takes his hand off the collective!
You hear the engine wind down and the rotor RPM drop.  He announces a gearbox failure.  So why did the engine wind down?  His passenger even asks if he switched the engine off.  If the gearbox had seized, the engine would have been destroyed or, the input shaft would shear and the engine RPM would increase leading to a very rapid overspeed.  There is no gearbox failure mode that results in the engine winding down.
He had a long think and a bit of a chat after the engine and RRPM wind down.  In a Bell 412, with the speed of that wind down, the blades would have stalled after 2 or 3 seconds if he hadn't dropped the collective.
He announces that he is going to autorotate.  His passenger asks "auto what?"  He says we're going to crash.  The whole point of autorotation is that you don't crash.
With the RPM already low (let's forget that he would have stalled by now), his first action is to dive and you hear the RRPM increase.  In reality, they would go even lower.  If he wasn't already stalled (which of course he would have been) he would now.
He was straight and level, with significant airspeed over level open ground.  At the first bang and sound of the engine winding down, he would have lowered the collective and flared to preserve RRPM. He would then look for a good place to land, not a shopping centre car park, and fly towards it.
Each time he flares, he pitches forward again and the RRPM drop rapidly.  Flaring like that in auto would cause a large increase in RRPM, possibly overspeeding and lowering the nose to the level would cause a small drop in RRPM.  Diving again would reduce the RRPM.  So why would you flare to increase, then dive to decrease?

In short, the sequence is complete nonsense.

Excellent narration on everything wrong!  But per your first comment on the question: If one wanted to reduce distance traveled to land (e.g., one happens to be exactly over a beautiful landing spot during power failure) would a series of dives and flares ever make sense?  Or can you just flare to stop forward motion and then set the collective for a constant descent rate, floating straight down and yanking the collective at the end for a gentle landing?

Or what's the helicopter analog to the fixed-wing landing mantra "throttle for altitude, pitch for speed?"

@feetwet A series of dives and flares makes no sense ever.  If you are directly over the only safe place to land, then you have a few choices, depending on height.  If you have altitude to play with, you could perform a zero speed auto until about 3-400 feet, then pitch down to increase speed (you MUST have airspeed for the flare at the bottom) and use S turns to reduce distance over ground.  You could even start by going backwards so that you fly away from the chosen spot, then fly forward to gain speed for the flare.

The easiest, safest option is to simply S turn all the way down, maintaining airspeed and using the collective to keep RRPM under control.  If you try to go all the way down with no airspeed, you will arrive close to the ground with a high rate of descent and pulling enough collective to arrest that rate will stall the blades while you are still a long way up and you will fall 50 feet or more to the ground.  Airspeed at the bottom is life.  Not sure I understand your question about the analog for "throttle for altitude, pitch for speed".

Pitch for speed yes, but you have no throttle (the engine is dead!) and no altitude control. You ]control rate of descent somewhat but you are basically going down fast.  At 1000 feet, most non-helicopter pilots are surprised at how close the landing spot is (it's somewhere visible in the chin windows, not out in front) and how quickly you are on the ground (less the 20 seconds).  From 1000 feet, at max range airspeed, you are going to be on the ground in less than a mile.  A key point is that you extend the glide with airspeed, not with collective which is only used to control RRPM.

I should also add that increased RRPM and turns increase the rate of descent.

@simon if you're over the best spot, you can also make a 360 auto.

@rbp  Cough, cough, er, yeh, I'd forgotten about that one.  Thanks!

So there's some minimum groundspeed and minimum RRPM required for an autorotation landing, right?  (There must be a chart.  Is there a chart?)  Based on what you've said it sounds like the landing mantra would be, "Collective for RRPM, pitch for groundspeed."

You call out that the pilot takes his hand off the collective. In an earlier, even more idiotic scene, he puts the helicopter in "auto hover" mode and leaves his seat completely to winch someone up in the back cabin...... Idiotic movie.

@GregTaylor That scene is actually plausible.  Several helicopters have an auto hover mode, including the 412. https://www.youtube.com/watch?v=h2KPbKYXxyo

@feetwet Ground speed is irrelevant except for the last few feet when you need to land.  You fly by airspeed.  Speeds are in the pilots handbook for the specific model.  For a typical light helicopter, min rate of descent will be around 52 kts, max range about 62 kts. RRPM will be 95-105% with power, 90-110% in autorotation.


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What is this missile extended beneath an F-104 Starfighter?
On a video posted on YouTube there is a short clip of some sort of rocket-powered device - presumably a missile - extended beneath an F-104 on a mechanical sling. It must have been lowered into position, since the F-104 certainly couldn't take off with it in place.
I can't find any reference to it, and would like to know what it is.

device in place and ignition source

Supersonic store separation is a tricky issue. Using a trapeze makes it much more controlled.

The extending trapeze launcher was used with the Genie air to air nuclear missile on early star fighters. A similar design was use with F106 delta dart which had an internal missile bay.
https://en.wikipedia.org/wiki/Lockheed_F-104_Starfighter

There was a nuclear A2A missile? Was it in regular service?

@CptReynolds It was designed to attack large bomber formations and was fired once in an exercise, with Air Force observers right below the nuclear explosion.

I was stationed at Griffiss AFB in NY. we had a F106 fighter squadron located with us, the 49th FIS. They kept a pair of aircraft on alert fueled and weapons on board. Of course the USAF will neither confirm nor deny the presence of nuclear weapons on any base. I worked maintenance on the SAC side with B52G and KC135A aircraft. We also had aircraft on alert.

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Why divide the blades of a 9 blade propeller into 3 groups?
In a youtube video an airboat is featured with two contra-rotating propellers, each holding nine blades. Interestingly those nine blades are not spaced evenly, but grouped into three groups. I've never seen such an arrangement before, and I expected an evenly spaced configuration to be more efficient. What could be a reason to prefer this grouped configuration?

Even though this question is about a boat and not really an airplane, I still hope it is ok to post here!

Related if not duplicate: https://aviation.stackexchange.com/questions/43279/what-are-the-benefits-of-a-non-orthogonal-scissor-tail-rotor

Comment rather than answer since this is just a guess, but maybe they found it easier to build a propeller with three evenly-spaced groups of three blades each than to build one with nine evenly-spaced blades?

If there was a technical reason beyond "it looks cool", I would guess it would be some benefit noise wise, where it may sound more like a 3 blade prop than a 9 blade, and the resulting lower beat frequency of one prop, interacting with its counter-rotating mate, was less objectionable.
I went on a mangrove airboat tour in Forida once in a 454 V8 powered boat and it was earplugs PLUS ear muffs together for me, so I can imagine that anything that helps with noise levels while absorbing all that power would be very sought after.


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Do Airbus aircraft have an "off" position for their landing gear?
I know some Boeing aircraft feature an up, down, and "off" position for their landing gear lever. I know that some Boeing wide-body jets do not have a 3rd lever position, but still have an "automatic" "off" setting that takes effect after a time-delay (which begins when the gear comes up). Do airbus, bombardier, embraer, etc. have a 3rd gear lever position in any of their aircraft? If not, do they have an "automatic" off setting?

"Off position" for the gear or off-position for the switch that controls the gear? Do you mean as in "gear up / off / gear down"? Please clarify in your original post.

What would "off" even mean?

@ratchetfreak We have a question on that

I was working for Airbus before, never seen it on A300, A320, A330, A340, A380, A350 or A400M. Only Gear Up or Gear Down position.
For confirmation on A320, here the FCOM section:

NORMAL OPERATION
  The flight crew normally operates the landing gear by means of the lever on the center instrument panel. The LGCIUs control the sequencing of gear and doors electrically. One LGCIU controls one complete gear cycle, then switches over automatically to the other LGCIU at the completion of the retraction cycle. It also switches over in case of failure. The green hydraulic system actuates all gear and doors. When the aircraft is flying faster than 260 kt, a safety valve automatically cuts off hydraulic supply to the landing gear  system. Below 260 kt, the hydraulic supply remains cut off as long as the landing gear lever is up.

To summarize the FCOM, the system goes automatically to the equivalent of Boeing's OFF when airspeed exceeds 260 kts.

Im sorry for the unclear question. Regardless, it has been answered. Yes, what I meant was "gear up"/"off"/"gear down". According to the answer (much appreciated!) there is an automatic off position for the gear (hydraulic cutoff to gear over 260 knots). This is what I was looking for. I am sorry for writing an unclear question. Thank you Chris Lau!

This is incorrect for the A300. From the A320 onward, you are correct.

Yes, Airbus aircraft used to have an OFF position (called NEUTRAL) for the landing gear lever on the A300 and A310. As Chris Lau's answer shows, this third position was removed on the A320 and all subsequent models. Note however that there is no NEUTRAL label next to the lever (where Boeing would write OFF):

(4) Landing Gear Normal Lever:

UP: The L/G lever electronically controls the Green hydraulic supply for the L/G operation. The Green hydraulic system only is used for L/G retraction. When the lever is UP, the main wheels are automatically braked, during the L/G doors opening, through the ANTI SKID system, (the ANTI SKID selector being in NORM position) and without action on the brake pedals. L/G nose wheel is braked by a mechanical device.
NEUTRAL: When L/G lever is in the Neutral position, ANTI SKID system is deactivated and the L/G hydraulic pressure is cut off. Neutral position is normal flight position.
DOWN: When L/G lever is at DOWN the ANTI SKID system is operative.
Note: On ground, L/G lever can be moved from DOWN to Neutral position and vice versa, but interlocks prevent an inadvertent UP selection.

(Airbus A300 FCOM - Chapter 7 Landing Gear - Landing Gear Controls)

(1) Landing Gear Control Lever:
UP: The landing gear is retracted.

An interlock mechanism prevents unsafe retraction by locking the lever when gear position proximity detectors of selected SYS (1 or 2) are not in flight configuration:

3 shock absorbers extended
nose wheel centered
2 bogie beams aligned.

During door opening only, anti skid is deactivated and main gear wheels are braked automatically.
At end of nose gear retraction travel, nose wheels are mechanically braked.

Neutral: Normal flight position. Hydraulic pressure to landing gear circuit is cut off.
DOWN: The landing gear is extended and the system remains pressurized.

(Airbus A310 FCOM - Landing Gear - Controls: Landing Gear Lever Panel)

There are only two positions in the Embraer E-Jet family. There is also a downlock release button (red) which mechanically bypasses the system protection logic. It should be used only in the event of a landing gear control lever failure or when it is necessary to clear obstacles.


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What is the meaning of nose-art on the Tu-160 bomber?
The BBC reports another Tu-160 interception on 15 Jan 2018 and it's clear that there is a large message painted on the side of the bomber.
Looking at the Wikipedia page, it seems this style of nose-art is common among the Tu-160 community; the style is similar, but whatever it says, they're all different.
It would be interesting to know what's being said here, and who is making the choices. Official propaganda,  or personal messages?

(source: BBC)

Most Tu-160's are named after notable Soviet military pilots. English Wikipedia doesn't have a complete list; here's a link to the Russian version. Out of 16 currently active Tu-160's, 9 are named after military or test pilots and 4 after aircraft designers (including famous helicopter designer Igor Sikorsky). The rest, for some reason, bear the names of a famous Russian general, a Soviet wrestler champion and a Russian folk hero (though it may be a reference to WW1 Russian bombers of the same name). The names are official.
This one is named after Vasily Reshetnikov, a WW2 bomber pilot who later became head of Soviet Long Range Air Force (Link to the Russian Wikipedia article).
The nose colors are from the Russian Air Force or Soviet Air Forces flag:

(wikimedia.org)
Most of the Tu-160 in service are named, much like the B-2 bombers are.
The one in the image is S/N: 7-02 "Василий Решетников / Vasily Reshetnikov" named after a WW2 pilot.
You can find the names of the other ones on the Russian Wikipedia.

Both messages are Russian names: Vasily Reshetnikov (flew 307 missions in WWII mainly as a pilot for a long-range bomber, Hero of the Soviet Union) in this picture and Alexander Novikov (Chief marshal of the aviation for the Soviet Air Force, involved in nearly all exploits of the air force during WWII, twice a Hero of the Soviet Union) in Wikipedia.
Probably these texts are the names of persons notable in Russian aviation (not necessary pilots). They are different for different planes.


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How do conventional missiles fly?
With the exception of cruise missiles, most missiles don't have any obvious lifting device.
If you watch a missile being fired, prior to its rocket firing it does exactly what you'd expect: momentarily plummet toward the earth. And yet the moment it ignites, it stops falling completely, but without any pitch that you'd expect to counteract gravity; even big missiles like the Phoenix or HARM seem to have gravity-defying characteristics.
Missiles that fire on the rail seems to experience no drop at all.

AIM-9M launch from an FA-18F source
There's a good slow-motion video of the firing of an AMRAAM here.
Now this isn't magic, so I presume either a) the little fins make adjustments so that the rocket is, despite appearances, pointing a little downwards or b) the fins are smart enough to configure themselves to provide the lift needed to keep the missile in the air. But it might be neither.
The question is - generally, how do conventional missiles fly?

don't have any obvious lifting device - from the picture you post they look obvious to me - just because they're small does not mean they're not wings. Here's a toy radio control model "missle" made of foam: https://www.youtube.com/watch?v=v_wRls4aG78. It's controlled like a regular airplane with tiny wings

Bear in mind, if it's solid fuel propulsion, you really don't want it igniting while it's under your wing. You want it to fall away a few metres before flames shoot out of it.

"With such engine even barn doors would fly." - I was told that years ago about some soviet fighter jet with oversized engine, which seemed to be built like manned missile. Brute force can work miracles!

$PTwr: Would that have been the Je-166 by any chance? They took the biggest engine and added the smallest wings they could get away with.

Air-to-Air guided missiles are little airplanes. If there are only fins at the tail, it's a ballistic rocket, basically a fin stabilized artillery shell accelerated by a rocket motor instead of an explosion in a pipe.
On missile like AMRAAM, Sidewinder, or Sparrow, the vanes are wings and the missile is a rocket powered aircraft that can climb, descend and turn as required.  The vanes/wings don't have to be very big because the thing is going superdupersonic.  The X plan form means the wings can support and control the missile equally well in any axial position.
The front vanes are movable and do the controlling.  It's effectively a rocket powered robot canard aircraft on a suicide mission, really.
Since the missile accelerates to >Mach pretty quickly and operates supersonically, the wings/vanes use a supersonic airfoil profile, either biconvex (like the F-104's airfoil) or a diamond profile.  The vanes on the AIM-9M look like biconvex airfoils.
The missile descends when it is first launched because it's going too slowly for its teeny tiny supersonic wings to do enough lifting, and has to accelerate first.

Now, for a change of pace, slow something like an AMRAAM or Sidewinder down to subsonic speed, make the fins bigger and provide control surfaces on the rear ones, power it with a turbojet instead of a rocket except for boosting it into the air, and you have the CL-89 surveillance drone, basically a reconnaissance cruise missile that flies hither and yon at low level taking pictures.

Also for "going superdupersonic."

Re, "...it's a ballistic rocket...", Ballistic means unpowered. A ballistic missile gets a big kick from its booster at the start of its journey, and then for most of the way, it's just a dumb, thrown object.  Guided missiles (including cruise missiles) are powered the whole way, and use vectored thrust and/or moveable airfoils for steering and lift.

No ballistic just means it's travelling an arc that is determined by velocity and gravitational pull, falling as it moves in other words.  A rocket with fixed tail fins is a ballistic projectile, the motor running or not, once it leaves the rail.

@JohnK, so essentially what you are saying is that the faster you go the smaller wings you need to generate enough lift?

@ZeroOne yes that's pretty much the case for most airplanes.  Go fast enough and you can get enough lift from just the body alone although it's still nice to have wings/vanes to maneuver.  You don't necessarily have to go that fast if you have a large enough area; seaplanes get enough lift from their floats to be able to cancel out most of the floats' weight and there is only a small useful load reduction if at all.

This answer does a good job of answering the "They don't seem to have wings" part of the question, but doesn't discuss the impact thrust has on the question. Strap a powerful enough engine to anything and you can make it "fly"

@SolomonSlow Think ICBM. That's intercontinental ballistic missile. No, you don't shoot an intercontinental missile from a big gun. Although now I'm curious if that was ever done. Probably not.

@Nobody, An ICBM takes approximately 45 minutes to reach its target. Its flight is powered during maybe the first three minutes of that time. Except for small course adjustments using RCS thrusters while above the atmosphere, it basically is a dumb, thrown object for almost the entire flight.

The missiles in this answer are all guided, not ballistic. If their course was only effected by gravity they would be unable to strike targets at higher altitudes. An air to air missile that can be evaded by a hot air balloon is useless. [ Also, submarine launched ballistic missiles are expelled via compressed gas because of the obvious drawbacks of igniting a rocket motor inside the launch vehicle, making them effectively shot from a big gun as well as yielding ballistic->powered->ballistic flight paths.)

@Matthew Gauthier: That's simply not true.  Missiles, whether guided or not, don't NEED lift. (Though some may use it.) The fins are for directional control.  Strip the fins off, set the missile on the ground pointing upwards, and light the fuse, andI guarantee it will go up.

@jamesqf Any guided missile has to make lift somehow, to fly in any other trajectory than a ballistic arc, or straight up.  It may get lift off the body alone if it's operating at a positive angle of attack but it won't be able to maneuver much or fly efficiently without the little wings that are the fins.

"rocket powered robot canard". I know it doesn't mean that but I still picture a suicide duck.

@JohnK, think vectored thrust.

@SolomonSlow All vectored thrust can do is provide a yaw/pitch moment independently of a control surface.  If you want your missile to fly horizontally in level flight it still has to generate lift somehow, using wings, the body of the missile itself, or a combination thereof.

@John K: No, the missile does not have to make lift, in the sense we think of lift as something keeping an airplane airborne.  It uses fins to provide directional control, but a missile could use vectored thrust, reaction control jets, gyroscopes, &c for the same purpose.  Indeed many large missiles don't have fins, so they have to use other types of control.

@jamesqf Show me a missile with no fins, or tail fins only, that relies on vectored thrust or movable tail fins only, that can make sharp turns at high speed, because that's what we are talking about here.  Perhaps the term "guided missile" is too broad because that includes ballistic missiles that can alter their ballistic trajectory to some degree.  What we are talking about here are missiles that can turn sharply while in level flight.

@John K: Leaving out the "sharp turns at high speed" because that isn't one of their design criteria (and it's not what we're talking about, either), how about the Atlas, Delta, Saturn, SpaceX's Falcon...  down to the "rockets" I made as a kid by wrapping aluminum foil around a match, with a pinhole for the exhaust.  The fins are used for directional control, like the rudder/elevator of an airplane, not to produce lift.

@jamesqf well the discussion here is about missiles fired from jets that fly horizontally and maneuver to hit a target.  "Guided missile" is probably not a good term to use because that includes ballistic missiles that fly ballistic trajectories but can alter their trajectories to some degree and can therefore be considered "guided".  AMRAAM doesn't go in a ballistic trajectory.  It flies, horizontally.  It turns, quite sharply, considering.  In its case the fins, and the missile's body to some degree, are creating lift and it's effectively a rocket powered aircraft.  That is the point.

This is one of the best answers I have ever read on Stack exchange. Not just in terms of content.but the writing style as well! Even a 5 year old can understand it!

@John K: Not the point, because missiles in general (of course there's a spectrum with cruise missiles at one end) don't need lift, and often aren't using it.  The ones with fins are using aerodynamic forces to control their direction.

The missile's wings are very large for it's mass, and produce a great deal more lift than the wings of the aircraft firing the missile.
One thing to note from the OP's linked video is that the F-35 and the chase plane are traveling at the same speed, so the F-35 appears stationary. However, that aircraft is likely traveling in excess of 0.8 Mach. Therefore, upon release, the missile is also traveling at 0.8 Mach. The large wings provide plenty of lift. Some missiles may thrust vector as well.

In the video you posted, the  missile appears to continue falling even after the motor ignites -- you can see the  missile start to overtake the aircraft even as it continues to drop:

By the last frame, it appears to have taken a slight nose-up attitude to maintain altitude:

That dropping down is desired and enforced by a negative angle of attack on the missile fins. Look here what can go wrong.

@PeterKämpf - Hmm yes, I can see why shooting yourself with your own missile would be undesirable.

Either this answer only applies to the initial phase of the flight (so it's not really an answer to "how do missiles fly?") or it suggests that missiles continue to free-fall as they fly, which is simply wrong.

@DmitryGrigoryev - I was mostly addressing this point in the question: And yet the moment it ignites, it stops falling completely, but without any pitch that you'd expect to counteract gravity, which is clearly not the case in the video he linked to.

Depending on the range and mission of your missile, body lift alone may be enough to keep it aloft.
@dotancohen pointed out that a typical missile's wings are large for its mass, but look at the ASRAAM - it has only small tail fins which are there purely for attitude control, rather like an AIM-9X (which already has much smaller wings than the 9M) but with even fewer lifting surfaces. It's extremely slender to reduce drag, probably with the intent that it should retain as much of its energy (and thus speed) as possible. With enough speed, you'll only need a little AoA for the missile fuselage itself to create sufficient lift. This seems to be a typical strategy for short-range missiles, but the ASRAAM takes it to the extreme.
Missile meant for longer-ranged engagement may employ a lofting profile during the boost phase, opting to use the rocket motor to gain altitude as well, in which case the thrust will directly offset some of the weight of the missile.

gotta keep that attitude in check.


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Why is this F/A-18 flying through a hailstorm of sparkles?
The F/A-18 Super Hornet squadron VF-102 Diamondbacks, flying from the USS Ronald Reagan, has posted a montage video of its 2019 Indo-China cruise.
At about 5:15, the video shows a night-time cockpit view of the aircraft flying through a shower of sparks. There is also the view looking backwards. It's like a sci-fi special-effect.

What would cause this phenomenon?

source - YouTube

Illuminated rain drops appear almost horizontal due to the speed ?

That's what it looks like when you light the afterburner and go into hyperspace.

Flying thru rain or snow at night with landing lights on totally gives the sci-fi "warp speed" effect looking forward. Dunno about the part looking aft. The segment is playing at many X normal speed. Might just be rain drops in the aircraft's red lights, but that's only a guess.

Is that scene of the video in real speed or time-lapse?

Jorg, Ralph - I think Jpe61 is correct about it being gunfire residue so no the video isn't speeded up. You can see something very similar here https://www.popularmechanics.com/flight/a23060/super-hornet-cannons-hyperspace/

My God, it's full of stars!

The sparks in the video come from the F-18's Vulcan cannon being fired at night.
During daytime you'd only see muzzle flash accompanied by a pretty puff of smoke. Low light conditions bring out the sparks, or rather, residual gunpowder still burning (or glowing) as it exits the barrel.

Interesting - looks spectacular. I remember seeing this documentary about the St Elmo's fire experienced on BA Flight 9, June 24, 1982. Also very strange to look at. Air Craft Investigations / Mayday - Season 4, Episode 2 (2007).


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Can a pilot initiate an enroute descent to an IAF without ATC 's approval?
An IFR flight is cleared DIRECT to a published IAF for an approach at the destination airport. The cruising altitude is 10,000’, the IAF crossing altitude is 2,000’ and the T/D begins about 24nm prior to the IAF with standard rate of descent.
Since route has been previously cleared to that IAF waypoint, can the pilot commence his descent upon reaching the T/D, or wait to hear from controller or request descent instructions just prior to the T/D?

You are never allowed to simply vacate an assigned IFR altitude without clearance.  When you were cleared to the IAF your clearance should have included "pilot's discretion down to ..." of "cross IAF at or above..." or similar words.  If you don't get this, just ask.  Never presume that you can just start down on your own though.

No, you can not descend from your assigned altitude until specifically cleared by ATC to descend. But yes, you can descend down to  your Approach without further clearance given you meet a few parameters
First, make sure you are cleared for the Approach itself and not just cleared direct to the waypoint. Your assigned altitude is mandatory until you are established on your cleared Approach. Established means that you are on or immediately about to be on (less than a mile of) a published leg of the Approach. Once you are established on your published leg, you can descend to the at or above altitude published for the route.
If the altitude has a line above and below it, you must be exactly at the published altitude. If that is the case, you will be verbally stepped down to the altitude by ATC.
If the IAP includes a published Terminal Arrival Area, and you are cleared for he Approach, you are considered established on the approach when you are inside of the TAA’s lateral boundaries. The altitudes published for the TAA will dictate your altitude limits you have to remain above.
If ATC does not expect you to follow the IAP exactly to include its published altitudes, they will not clear you for the Approach. They will continue to vector you and give you altitudes.

The clearance given in the OP allows you to proceed direct to the IAF waypoint, but it does not clear the pilot to deviate from the currently assigned altitude, nor does it clear the pilot to fly the approach.  These would require separate ATC clearances.
The route at your assigned altitude has been cleared to you - you do have that block of airspace - but not the airspace above or below it.  Think in 3 dimensions.  Now you may inquire about starting a descent at that point with ATC, but would need a specific clearance to do so.


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How many African countries currently deploy Cat 3 ILS?
How many countries in Africa currently operate Cat 3 ILS?

I think this will answer your question:https://aviation.stackexchange.com/questions/71602/is-there-a-list-of-airports-with-category-3-ils-systems

What have you searched for so far?  It seems that this might be relatively simple to find online.

Does this answer your question? Is there a list of airports with Category 3 ILS systems

This answer has a list of all airports with a Cat III ILS system.
Africa was assigned ICAO region codes D, F, G and H, so you can just look for ICAO airport codes on the list starting with those letters. The only one I see is "GMMN (MOHAMMED V INTL) on runways: 35L, 35R". That name wan't familiar to me, but a quick Google search says that GMMN is Casablanca, Morocco.


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What is the purpose of the box between the engines of an A-10?
There is a curious box between the engines of an A-10. It's seems rather rudimentary, like an afterthought, although it was present on the prototype.
I've found a few cutaways but this part is hidden. I'm fairly sure that at least the front is hollow, so perhaps related to an APU. The question is, what is it for, and why, even in the context of the somewhat inelegant A-10, why so unrefined?

source: savasucakalari

I feel like there is an identical question around here for some reason but I can't seem to find it!

It is the intake/exhaust duct of the cooling system.
Basically, the front side consists of the ram air duct, which feeds air into the ECU precooler, with the (heated) exhaust air vented out through the rear. The image below shows a closeup of the duct.

Image description: Kenneth Thompson, 576th Aerospace Maintenance and Regeneration Squadron aircraft mechanic, aligns a portion of the pre-cooler ram air duct onto the top of an A-10A Thunderbolt on Davis-Monthan Air Force Base, Ariz., Jan. 23, 2013. Source: warthognews.blogspot.in
Here's another image that shows a cross-section of the system. The cooling system (without the box) could be seen above the APU.

Image from pintrest.

I wonder if you can shine any light onto the the boxy design of the duct? Airliners etc. tend to have intakes built smoothly into the side of the airframe. I'm assuming this one is on top to reduce the chance of dust and foreign objects from getting in?

@Cooper I think it's simply the consequence of the location of ECU. The front of the aircraft is dominated by the massive GAU-8. This along with the location of engines, have meant that the ECU, APU etc. are in the rear part of fuselage. And you'd be right that the location is to reduce chances of fod ingestion; also A10 being purely designed for CAS, it wasn't fine tuned for drag reduction, though my guess is that the contribution of the 'box' to drag would be negligible.

Nah, it's just there so that guy has something to hang on to if the pilot takes off while he's still there. *nodnod*

It's an intake (front) and exhaust (back) for the cooling system.
Sources: Photographs, diagram.
However I can't for the life of me find any reference to its unusual boxy design. Perhaps it simply doesn't need streamlining because the A-10 is designed for relatively low-speed flight.
The position of the box is probably high up (much like the engines) to reduce the chances of dust and foreign objects from clogging the intake, as the aircraft is designed to fly at very low altitudes.


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Why was Energy Maneuverability theory not applied to the F-14?
In John Boyd's (declassified) 1966 Energy Maneuverability [PDF] report, studies were done on the F-4 and on the MiG-21 and those studies were applied to the F-15, F-16 and F-18. My questions:

Why wasn't this theory applied to the F-14?
Was this due to the fact that it was a carrier-based aircraft?
Or did it have to do with the variable sweep wings that would change how the energy bleed changed with changes in the sweep angles at different speed?

The F-14 was developed well before the theory of Energy Maneuverability was published, but improvements were made in F-14s till the late 1980s. With the early development of F-15s the Energy Maneuverability theory was utilized to improve its performance but same wasn't done or at least mentioned anywhere.

F14 simply wan't quite optimized based on EM in the beginning and there's so only so much you can do afterwards. E.g. can you really remove the sweep wing and make more weight budget for the engines?

Actually, there is an optimum sweep position varying with Mach and lift coefficient. The F-14 had computer controlled sweep which did exactly that, optimize sweep for the current flight condition. The claim that energy maneuvrability theory was not applied is bunk - it just wasn't called that way.

The most significant consequence of EM theory is the emphasis on the engine. F14 only has a barely usable 1st gen turbofan and have already done its best. EM is only practical after the next generation of engines enter service.

The Energy Maneuverability theory is primarily a conceptual design framework. Its role is to be a guideline in creating the requirements for your aircraft.
This is something well above the manufacturer's level of responsibility. The requirements are created by the buyer, like the US DoD; the manufacturer's job is to design a machine to meet them, with some leeway. And not all modern fighters are based on the E-M theory.
It's not impossible to use a new design framework if you were doing a Hornet to Super Hornet kind of 'Hollywood remake'. But otherwise, an aircraft is created to do a job, and that general job persists through upgrades. Every design choice is a compromise; to get more of X, you need to lose some of Y. Only with a major technological leap could you fit more of X without that loss.
The F-14's job was to maintain long-range CAP around the CVBG. It needed to detect incoming Soviet aircraft at the longest possible range and intercept them before they could launch their missiles.
The USN had very good reasons to dedicate their top fighter to this role. While the Soviet Navy (VMF) has never been a force the USN had to reckon with, the Soviet Naval Aviation (AVMF) has. Its workhorse was the Tu-22, a supersonic bomber with AS-4 missiles; they're large enough to take out a carrier, and, impacting at Mach 3.5-4.5, outside the realistic capabilities of contemporary SAM, AAM and CIWS to intercept. With a standoff range of over 300 nmi, AVMF bombers would be out of the reach of the Californias at the time of launch. This left CAP essential to carrier survival.
For this job, a fighter needs several things. It needs the range and endurance to patrol far enough from the carrier to help. It needs a powerful long-range radar to spot it before launch. It needs good supersonic speed to have a shot at a Mach 1.8 aircraft. It needs to carry heavy long-range missiles to reach the target.
You'll notice that dogfighting a Mig is not on the list above. It's certainly within the F-14's role, which it performed successfully in Iran, just not as critical as fleet air defense.
Attack roles aren't in that list either. In the 1970s, they have been mostly filled by Skyhawks, Intruders and Corsairs. The F-14's design, including its swing wing, was a product of its high speed interception requirements, combined with low-speed needs of taking off with limited power and maintaining long patrols.
Even if the E-M theory was fully developed and accepted at the time, it's not likely that following it would have improved the F-14's performance without compromising its primary role. With the end of the Cold War the requirements changed, freeing up the F-14's carrier slots for multiroles with an offensive focus.

Develop a carrier based aircraft to protect a carrier to transport a carrier based aircraft to...

...To do all sorts of things. Three dedicated strike fighters served contemporarily with the F-14's fleet air defense career. Plus, the F-14 soon got its own strike capabilities, if limited. But its primary role has always been protection. You design for the worst-case scenario, the best case is easier to take care of.

@jean As Therac said, you're missing the idea of multi-weapons cooperation: strike aircraft needs to be protected by fighters, and all fighters need logistics. ANd fighters will protect logistics.

And it should also be noticed that F-14 performed well against other aicrafts, such as in Iraq-Iran war. By the way, did they fight against MIg 29 during this war?

@totalMongot No, the MiG-29 was way too modern. Iraq only had older MiGs. But the F-14's were the only  fighters to have killed any Soviet-built aircraft. Everything older had no success. So the teen series were a necessary and major step forward for the US.

Oh you're right, according to this article https://theaviationgeekclub.com/iraqi-mig-29-pilot-explains-how-he-was-able-to-shoot-down-a-raf-tornado-during-operation-desert-storm/ there were Mig 29 in Iraqi air force but they did not fight Iran

Iraq basically got their Mig-29 after the Iran-Iraq War was effectively over. Otherwise the kill balance would likely have been very different - the 29's avionics are way ahead of Mig-21 and -23, which already got a few F-14 kills, and it's got F-16+ performance. During the Gulf War, Iraqi Air Force mostly retreated, so there was little actual combat.

In my understanding, EM is not a serious 'theory' that can be 'incorporated' in the aircraft design. It tells nothing new to engineers, even in the 60s. Rather, it is a convenient tool to evaluate (some aspects of) fighter aircraft performance and therefore to develop the most appropriate combat tactics. This is a typical situation with pilot-centric theories and data in general.
So in terms of such evaluation, it probably was applied to F-14 and many other aircraft at some point. If the formula gives a reasonable prediction of outcome, why not use it? That's very much the task of Air Force.

It's not becaue the F-14 has variable sweep wings or is a carrier aircraft.
EM works just as well for variable sweep as for fixed wing. EM is a measure of the excess energy available to climb or accelerate, in a dog fight. That physics principle isn't changed by having variable swing wings or being a carrier aircraft because laws of physics which describe these aspects such as F= m x a and PE (potential energy) = m x g x delta(h) still apply.
(I'd normally post this as a comment, but comments that are seen to be answers get deleted, so, sorry for a half-answer... I expect someone will provide a more complete answer.)

So later variants of F-14 would have incorporated EM theory. This would be de facto hence not mentioned anywhere, right ? But then why does use of EM theory in F-15 is much emphasised ?


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What is the difference between the flight control systems of different F-16 models?
It is mentioned that the F-16 A/B variants had an analog flight control system (FCS), while the C/D versions introduced a digital FCS starting from block 40.
Can somebody elaborate on the differences between them and point me to some reference?

Analog, as in measuring a signal like voltage of an op-amp, length of a slide rule, liters of fuel in the tank. Digital, as in: this car has four wheels, plus one in the boot.

Analog electronics are the original way that control loops were constructed.  They are blazingly fast, but:

they drift;
they are subject to external distortion like electro-magnetic interference;
they require tailored construction, as shown in the pic above from the Wiki article

At Fokker Aircraft, Control Loading Systems were constructed and marketed for flight simulators, starting in 1979. At the time analog electronics were the only option to provide the feed-back control loops that were required to load the simulator flight controls for any aircraft type, civil or military, fixed wing or rotary wing. So for every aircraft type, a dedicated electronics board had to be designed and manufactured in the Fokker electronics factory, an elaborate and expensive exercise.
The analog electronic components would have a finite life-time, then have to be trouble-shot and repaired. Here's another advantage of digital electronics: after debugging they always work in identical ways, unless the whole processing loop fails which is easy to troubleshoot.
Digital control loops provide good robustness to noise. For instance in the digital on/off signals of morse code, as long as we can hear some sort of dot the rest of the audible noise does not matter much. There are definite advantages to digital control despite the specific oddities they bring along such as added loop gain instability, plus changes are now a matter of adding lines of code and re-compile instead of soldering.
The F-16 fly-by-wire systems introduced in the early 70s were a marvel of technology, providing artificial stability and g-limited flight dynamics, as mentioned in this answer. Analog electronics were the only available choice, there were four control systems installed that compared their outputs and could detect a failed system, and disconnect it.
More information on F-16 analog vs. digital can be found here, interesting discussions from people with hands-on experience.

 The  main difference  is  processing speed, with the digital FCC's being faster than the analog models ( the analog-equiped aircraft it takes their FCC longer to detect the over-G, determine a correction, and send the correction to the actuators)and that's why first blocks until the 40 blocks will show +9G in the HUD .

Thanks, I meant more for the internals, how is it built, with which components. I heard that the analog system was basically built with "and" and "nand" gates.

AND and NAND logic gates are digital devices. The analog equivalent is the operational amplifier or op-amp, which can be configured to perform many different mathematical functions.

In general, being analog does not imply that the system is slower. On the contrary, analog systems can potentially have 'unlimited' performance (limited only by the speed of light), whereas digital systems invariably have processing delay. Analog systems don't work in the paradigm 'read, calculate, send; repeat': everything happens at once. Until processors became quite fast, analog systems performed better. Their main problem is that their complexity grows at least linearly with complexity of the task performed.

Zeus, that is correct. And with the flexibility of digital calculations, aircraft CGs could be moved backward to areas that a human couldn't control the aircraft, and too complex for analog designs, leading to more agility. [apologies, due to my very first posting, it does not allow me to comment to Zeus]


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Are STOL kits that use leading edge slats available for 'typical' GA aircraft?
Has anyone tried fitting leading edge slats to any of the 'typical' general aviation aircraft? If so, are the benefits worthwhile? I know they're available for the Piper Super Cub, but I haven't been able to find any for tricycle gear aircraft like a Cessna 182 or Piper Comanche. I know that having a  high wing or low wing will also be a factor.
The Helio Courier, a well known STOL aircraft, has a speed range from 25 knots to 147 knots. I assume that other aircraft may benefit for using leading edge slats or other devices to lower the stall speed to 25 knots or so, leading to slower, safer landings and emergency landings. All the advantages of the Helio, but in a different form that some people may prefer, for example the low wing aircraft configuration.
The only disadvantages I can think of are the limits of the tricycle landing gear in achieving a high enough angle of attack when landing due to the possibility of tail strikes, and the better protection from debris
in soft field takeoffs and landings.
And what would happen if someone fixed a Helio wing on a Piper Commanche, assuming cost no object?

Lowering stall speed is not a benefit in itself, it's only a benefit if it you need it. There are STOL kits for many airplanes, you don't see them much on most airplanes because there's no real benefits in normal flying and they cost a fair chunk of money to install. STOL kits only get you so far, adding a STOL kit onto an airplane with a 50 kt stall speed will not give you a 25kt stall speed, it's a lot less than that. If you have a bush airplane, fly into very short fields or in high density altitudes then a STOL kit can give you extra capabilities. If you don't fly into very short fields then a STOL kit is extra weight and costs for capabilities you won't use.
It's also not as simple as simply sticking some extra bits on the front of the wing, there's many considerations. For one, if you drop an airplane's stall speed substantially then you will run into control authority issues at slow speed. You will have to beef up the ailerons, rudder and elevator to compensate, which is a substantial re-design, adding costs. The most popular STOL kits are for airplanes which already are good STOL aircraft to begin with and have adequate control authority.

I should add that there are several aftermarket STOL kits, for example the ones offerred for the Cessna 182 and listed in this 2000 AOPA article: https://www.aopa.org/news-and-media/all-news/2000/december/pilot/the-skylane-mod-market


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Why do most radial engines use an odd number of cylinders?
To help suppress vibration, most 'V' and 'horizontal' engines use an even number of cylinders as closely opposed as possible. Radial engines are well known for excessive vibration. For some reason they nearly always use a staggered odd number of cylinders that would seem to promote vibration, why?

V engines have even number of cylinders by definition.

@Agent_L, you can get a V5 engine. I've no idea if they're used in aircraft or not but VW use them in cars.

@Holloway VW calls it "VR engine", not "V engine". It's pretty much a staggered inline (R stands for reihen, meaning inline here), not having much in common with V engines except superficially similar cylinder layout.

@Agent_L / Holloway - Its always interesting to learn the exceptions to the rule; just when you think you pretty well know a subject completely. Thanks for the additional info.

By definition, V engines have cylinders arranged in a V.  The V designation has absolutely nothing to do with the number of cylinders.

An odd number of cylinders is required by the combination of the single-crank radial design, the four-stroke (Otto) work cycle, and the desire to keep the power strokes evenly spaced in time.
To keep the design simple and lightweight, a single-bank radial airplane engine has one crank, which means that the pistons must reach the top of their travel in rotation order. But the four-stroke cycle requires that a piston must reach the top of its travel twice for each power stroke. The only way to promote evenly timed power strokes is to fire every other cylinder in rotation order.
With an even number of cylinders this would require a hesitation or skip in the firing sequence on every rotation as the engine switched between the odd and even cylinders. With an odd number of cylinders the timing is quite naturally smooth. For example, the firing order of an eight-cylinder radial would be
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
*   *   *   *     *   *   *   * *   *   *   *     *   *   *   *

while the firing order of a nine-cylinder radial is
1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9
*   *   *   *   *   *   *   *   *   *   *   *   *   *

If you could watch a radial airplane engine in slow motion you would see that when a cylinder is in its compression stroke, the cylinders on either side of it are in their exhaust strokes, and when a cylinder is beginning its power stroke, the cylinders on either side of it are near to beginning their intake strokes.
Two-stroke radial engines do not need to have an odd number of cylinders.

+1, couldn't explain it any better. For an example of two-stroke radials with even cylinder count the Zoche diesels come to mind. And to study the motion of a radial in slow motion I recommend the CAD models in the enginehistory.org site. Caution: The last link is to an animated GIF which takes some time to load.

How many cylinders are required in order to have two cylinders fire simultaneously - is it 7 or 9?

@jwzumwalt: A single-bank single-crank radial can never fire two cylinders simultaneously.

@jwzumwalt infinite cylinders are required.

An odd number of cylinders is required by the combination of the single-crank radial design ....weeeeelll, technically, isn't a flat/boxer twin a "two cylinder radial engine"..?

@Grimm The Opiner: Infinity is not possible. As the number of cylinders approaches infinity, their firing sequence approaches simultaneity. - Interestingly, in addition the size of the aircraft approaches the size of the universe, obviating the need to take off.

@Grimm The Opiner: You may call it a radial. I call my little Briggs&Stratton lawnmower a "one cylinder radial" but that don't make it a simple lightweight airplane engine.

@Grimm The Opiner: As per my first paragraph, one of the three criteria that forces the odd cylinder count of a traditional radial is the single crank. A boxer twin has two cranks.

@A.I.Breveleri Well, whatever kind of twin a BMW motorcycle is then. In bike-land they're generally referred to as boxers because the pistons punch "one-two". I love the single cylinder radial! Not least because it's the only radial engine wherein all cylinders fire at once - made possible because it has a crank per cylinder.

"if you could watch...": we can watch a radial airplane engine in slow motion, showing the firing order too

So clever!  What a great post.

"technically, isn't a flat/boxer twin a "two cylinder radial engine"" well no 9assuming you mean the boxer in an alfa): nothing in it is radial.  it is four lines tangent specifically to rectangle, not a circle.    lawnmower .. "one cylinder radial" sure, it's perfectly reasonable to call a 1-cyclinder a "radial" - because the one line we can assert is tangent to some circle, it is.  The four lines of a boxer simply are not tangent to a circle, so there isn't even a humorous sense in which it is a "radial".

The biggest reason for the high vibration level from radials (especially single-row type) is that the entire mass of the crank pin, all the connnecting rods, and all the pistons is circulating around the crankshaft in unison.  Even with a heavy counterweight on the crankshaft (generally the case) the front-back imbalance is inescapable in an engine that can be disassembled for major service.

Is even timing really important? Isn't it very common to have uneven firing on car/motorcycle engines?

@user3528438: Yes, a smooth firing order is important for piston aircraft engines. Uneven firing applies a vibration through the same mountings and in the same direction as the main forces of the engine on the aircraft. Any springs or elastic grommets in the engine mounts are compressed by these main forces in exactly the right direction to maximally transmit the pulsing vibration.

@A.I.Breveleri None even firing doesn't imply vibration. Also, all of the V engines non-even firing, so what about Merlin?

user3528438: I sincerely hope for the sake of humanity that you are asking out of pure curiosity and not because you intend to design an actual airplane.

It is possible to have a smooth firing order for an even number of cylinders so long as the number of cylinders is not a power of two. Simplest example is therefore a six-cylinder radial with a firing order of 1-2-5-6-3-4. Power pulses come alternately every 60 and 180 degrees of crankshaft rotation (work it out). Think of it as two superimposed three-cylinder engines sharing the same crankshaft and rotated 60 degrees from each other. A ten-cylinder similarly would have a firing order of 1-2-5-6-9-10-3-4-7-8, with power pulses alternating between every 36 and 108 degrees  This would actually be quite smooth as the power pulses are not instantaneous and sequentially firing cylinders would have considerable overlap in their power strokes, especially with a 10 cylinder design.
A V-engine analog would be a 12 cylinder with a bank angle of other then 60 degrees.  Since a straight six has perfect primary and secondary balance, so does a V-12 at any bank angle.  Only bank angles that are multiples of 60 give all equally spaced power pulses, but with other bank angles, the engine is still perfectly balanced and smooth, the power pulses just come at gaps that alternate back and forth between two values just like a six, ten or twelve cylinder radial would.
Such a six cylinder radial would have an interesting sound at idle, no doubt. It would have a boomboom-boomboom-boomboom rumble, similar to but faster than the "burble" of a cross-plane V-8, but there would be no uneven "hiccup" as the gaps between both sequential cylinders and cylinder pairs are evenly spaced although different.  At speed, I suspect a 10 cylinder would not sound any different than a 5 cylinder, the sound of sequentially-firing cylinder pairs blurring together.
Engines with a power-of-two number of cylinders truly can't be built to run smooth, as they can't be timed as a set of superimposed engines with an odd number of cylinders since powers-of-two have no odd divisors.  For them, there will always be a gap in sequential power stokes once every two crankshaft rotations that doesn't match any other gap, a "hiccup" that could probably cause a lot of vibration.

+1 Interesting theory -- timing an even-numbered engine as a set of superimposed odd-numbered engines. This would probably be practical for 6, 10, 14, or even 18 cylinders. A 12-cylinder, however, must be timed as four 3-cylinders, which makes the groups of power strokes 4 adjacent cylinders long, with only 3 groups per rotation. This would probably be noticeably rough. - The problem of not enough groups also appears at 20 (four 5-cyl) cylinders, 24 (eight 3-cyl) cylinders, and other impractically large sizes.

first of all not all V engines have even number of cylinders.
Honda RC211V uses a v5 (yepp, 3 cyl on one bank and 2 on the other) engine. i just do not have enough rep yet to answer there.
now, odd number of cylinders in a radial engine is required for 4 stroke engines only.it was well described why. but 2 stroke ones may not have odd numbers. allso if double ended pistons are used (rare engine concept) then it would be possible to fire 2 pistons at the same time.

Honda has a penchant for odd-number V-engines. The NS500 race bike had a V3 engine (2 up, 1 laid down) and also the MVX250 road bike which had the orientation reversed (1 up, 2 laid down).

Look at valve timing figures for a average four stroke and bearing loads this will give a clue as to the firing order and to make sure that only one cylinder would fire at a time and avoid bearing overload. As to vibration you have to have equal reciprocating forces in opposite directions but in the radial this cannot be achieved without some sort of balancing shaft this would take valuable power and increase weight obviously

A even number of cylinders in one bank of a radial engine just does not work, purely for the fact that each cylinder has to fire once in every two rotations of the engine, as their is only one crank it is impossible to achieve a firing sequence that would work.
The firing sequence on a nine cylinder engine is 1 3 5 7 9 2 4 6 8, this provides a smooth production of power
Go to YouTube and look up “How a radial engine works”

Welcome to Aviation.SE! This does not seem to add anything to the existing answers.

Nor does it meet the standards for an answer. If you want to provide a link to a video, that would be an answer.


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How common is it for flight attendants to have pilot certificates?
When looking up some information for the recent question Have there been any solo flights on airliners?, I found this article that lists several incidents in which a pilot has become incapacitated in flight. One thing that I found particularly surprising was that, in two of the six specific incidents they mention, the person who helped the remaining pilot for the remainder of the flight was actually a flight attendant who had a pilot certificate. This then made me wonder:
How common is it for an airline flight attendant to also be a certificated pilot?

In my experience, it is uncommon but certainly not unheard of. Maybe between 1% and 5%, as a ballpark.  A flight attendant married to a pilot who owns his own aircraft has access to the plane and instruction, so that's one scenario. In another case, an F/A I flew with a few times was building time as a CFI and doing right-seat work at SimuFlight, before she left our airline to start with a regional. (Wouldn't be at all surprised if she's flying at a major right now.)
Among flight attendants, there are a lot of really interesting stories of how they got to be where they are. Sometimes the generalizations fit, but when they don't, you find an amazing breadth of experiences in that group.


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In the U.S., Is it ever legal for an aircraft to occupy the runway turnaround area while another is taking off or landing?
In voretaq7's answer to the question Is there a name for the area for aircraft to back track near the runway threshold?, it is mentioned that runway turnaround areas are considered part of the runway to which they are attached and that any aircraft in the turnaround zone are considered to occupy the runway.
I noticed that in the picture provided in his answer showing a runway turnaround area, the runway edge stripes actually included the runway turnaround area:

However, I've also noted that at the small, uncontrolled GA airport I've most often flown from, the runway edge stripes do not include the turnaround area:

Of course, in either case, a departing aircraft must cross the runway hold line and enter the runway to back-taxi to the turnaround area in the first place. However, I'm curious under what, if any, circumstances is it legal under the U.S. FARs for an aircraft to land or take off on a runway while another aircraft occupies the turn-around zone on that runway? And, of course, I'm talking about normal operations here, not emergencies.

Does the runway edge stripe configuration matter, for example?
How does this differ between controlled and uncontrolled fields?

For the sake of simplicity, let's assume that both aircraft in question are light GA aircraft, not aircraft whose wings might stick off the sides of the runway, and that all parts of the aircraft in the turnaround zone are on the turnaround side of where the runway edge line would be were it a straight line (like it is in the second picture.)
I have seen both landings and takeoffs with another aircraft in the turnaround area at the bottom field pictured above, including a couple of aircraft back-taxiing out there (under mutual agreement and while in radio communication with each other) and the second of them wait in the turnaround while the first takes off.

Jim's answer is accurate. Unless there is a proper boundary between the turnaround and the runway, an aircraft should not be there while other aircraft are landing or taking off.
In the FAA's AC about airport design:

Obstacle Free Zone (OFZ). The OFZ is the three-dimensional airspace along the runway and extended runway centerline that is required to be clear of obstacles for protection for aircraft landing or taking off from the runway and for missed approaches.

The dimensions of the zone are different depending on the aircraft size and approach minimums. Specifically the runway OFZ has widths from 120 to 400 feet. This is the zone typically protected by the hold lines (pictured in Jim's answer), which are typically placed to provide adequate separation for the worst anticipated case at that airport.
Regarding the edge markings, they should be parallel to each other and not follow the edge of a turnaround pad. From the AC on airport markings:

When a taxiway connects to a runway or the runway has turn pads or turnarounds, the runway edge marking remains continuous between the runway and these adjoining infrastructures.

If the turnaround pad is designed to be occupied while the runway is in use, this is referred to as a holding bay. A proper holding bay would look like this:

This illustration comes from the airport design AC. Notice that the FAA considers this poor, because it provides no guidance such as taxiway center lines for pilots to follow.

For non-towered airports, there is no such regulation. The only actual regulation that might prevent two aircraft from occupying a given runway at the same time is FAR 91.13, which prohibits the operation of aircraft

in a careless or reckless manner so as to endanger the life or property of another.

Want to line up and wait while someone else is rolling out? Touch down before the previous arrival has cleared the runway? They're not specifically prohibited - but neither is a good idea.
Depending on the size of the turnaround area, I would generally consider a landing while it's occupied unsafe - perhaps even reckless. However, a takeoff with the turnaround occupied might be comparable to a Line Up and Wait situation. The closest FAA guidance I can find comes from the Pilot's Handbook of Aeronautical Knowledge, in Appendix 1 - Runway Incursion Avoidance (p. 1-10):

NOTE: Line up and wait/holding in position is not recommended at nontowered airports.

That's good common sense. But "not recommended", in a document which is not legally binding, is far from an actual prohibition.

Why is it a bad idea to line up and wait while someone else is rolling out?

@pericynthion I had the same thought initially. But when you're lined up and waiting, you can't see behind you - another aircraft might be on final when you decide to start your takeoff roll. If you wait until the prior arrival clears, you can visually check final before taking the runway. At a towered airport this is less bad because the local controller should know who's out there.

The runway edge stripe does not define the runway boundary.  The runway boundary line defines the runway boundary.
Runway Boundary Line:

EDIT
For all airports right of way rules are covered in

14 CFR 91.113
(b) General.
When weather conditions permit, regardless of whether an
  operation is conducted under instrument flight rules or visual flight
  rules, vigilance shall be maintained by each person operating an
  aircraft so as to see and avoid other aircraft. When a rule of this
  section gives another aircraft the right-of-way, the pilot shall give
  way to that aircraft and may not pass over, under, or ahead of it
  unless well clear.
(g) Landing.
Aircraft, while on final approach to land or while landing,
  have the right-of-way over other aircraft in flight or operating on
  the surface, except that they shall not take advantage of this rule to
  force an aircraft off the runway surface which has already landed and
  is attempting to make way for an aircraft on final approach. When two
  or more aircraft are approaching an airport for the purpose of
  landing, the aircraft at the lower altitude has the right-of-way, but
  it shall not take advantage of this rule to cut in front of another
  which is on final approach to land or to overtake that aircraft.

For controlled airports with clearance from the tower multiple aircraft may back-taxi (usually two at a time) for departure.  The first aircraft will line up.  The second aircraft will wait in the turnaround area for the first aircraft to takeoff.
There is no rule explicitly prohibiting multiple aircraft occupying the same runway.  However the above regulation does provide guidance in answering this question.
Here are some uncontrolled airport scenarios...
Scenario 1:  Aircraft A is in the turn around area (not in a holding bay) preparing to takeoff.  Aircraft B is on final to land.  Aircraft B has the right of way.  Aircraft A is in violation.
Scenario 2:  Aircrafts A and B will depart on a group flight together (they have coordinated with each other prior to operating).  They both taxi to the end of the runway and line up for departure.  Both aircraft could take off in sequence with each other, or one aircraft could wait in the turnaround area while the other takes off.
Scenario 3:  Aircraft A is in a holding bay (explained in fooot's answer).  Aircraft B is on final to land.  Aircraft B has the right of way.  Aircraft A is outside the runway boundary and not in violation.
Scenario 4:  Aircraft A is in a turnaround area.  Aircraft B is on take off roll.  Aircraft B has the right of way.  Aircraft A must give way to Aircraft B until there is sufficient room to safely pass or Aircraft B is well clear.

What are we looking at in that picture. Please pretend for a minute that I'm an enthusiast only, and not a licensed pilot. :)

Do you know of any FAR (or similar) that would back up the assertion that only one aircraft is allowed on the runway at once?

@reirab, thanks for your comment.  I was incorrect and have amended my answer.

Thanks for updating the answer. I'm not sure I completely agree regarding scenario 1, though. Aircraft A certainly is not passing over, under, or ahead of aircraft B in that case. Also, for fields where there's a lot of runway between the turn-off point at the turn-around, aircraft A could have been (and likely was) occupying the runway long before aircraft B was on final... sometimes before aircraft B was in the pattern at all... with no chance of making it back clear of the runway in time for aircraft B to land.


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What is the source for the flight data shown on in-flight entertainment systems?
This question which claims that an altitude of 55,000 ft. was observed on a passenger's in-flight entertainment system on an Emirates B777 made me wonder: What are the normal sources of information for the flight data displayed on passenger IFE systems?
Of particular interest are the common sources for the following information:

Altitude (Is this a pressure altitude? Indicated altitude? A GPS-measured altitude? A radio-altimeter-measured absolute altitude?)
Speed (This seems to typically be true ground speed, which I'd assume comes from GPS, but any further insight would be appreciated)
Latitude/Longitude position (Is this from GPS? INS? radionav? some combination?)
Wind speed

There is no other source than the air data system of the aircraft. However, the data is filtered before it is displayed. The 55,000 ft altitude is not credible for several reasons.

I work on these panels which get the data (both IFE and cockpit display panels for a big OEM and there are very few in the world :)). This is all Air data systems which are providing all the data. We get this data from various sensors placed inside the cockpit or on aircraft exterior including wings and tail. Their are different kind of data transmission buses like ARINC which transmit that data then the required data is fed to IFE system through a protocol but most crucial data like data coming from Weather Radar etc is kept for Pilot usage and is displayed on the cockpit display panels.
For your question Altitude, elevation. azimuth there are some radars in the aircraft which gives that data and some of these radars measure and send this data using CAN protocol with very high speed varying from 40ms to 100ms.

Interesting, thanks! Can you elaborate on which particular data sources are used for the IFEs? For instance, as my question mentioned, the air data systems have several different sources that measure altitude in different ways (radar altimeter for altitude above terrain, GPS/INS for absolute altitude above sea level, pitot-static system for pressure altitude, etc.) I was curious which of these gets piped to the IFE systems.

After a brief search I found an old US patent that states:

The video display system of the aircraft is directed by the present invention to automatically display aircraft ground speed, outside temperature, and altitude, among other information of interest, as sensed by the aircraft's navigation and air data systems.

Hence I believe the information comes from same system that the pilots use, though the actual implementation may not be known to any of us outside companies that produce those IFEs.

My experience on a 757-200 owned by Icelandair this week was interesting. The Lat/Long DD:MM data displayed on the seat back display was OK for Latitude but wrong for Longitude. The aircraft Track was roughly NNW with a westerly component but showed the following bizarre series of positions:
18:02W    18:01W   19:00W    19:59W   19:58W  ........... 19:03W    19:02W     19:01W     20:00W      20:59W      etc
The degrees increment as expected, while the minutes decrement strangely.
Same bug observed on the return trip.  The degrees W decrement as expected, while the minutes increment.
Clearly this data is not a direct display of raw GPS data, but is being generated by the in-flight software presumably based on GPS input